1. Field of the Invention
This invention relates to infrared detection circuitry. In particular, it relates to a superconducting infrared circuitry for extremely low level signals.
2. Description of the Related Art
Superconducting circuitry is, of course, well known in the art. U.S. Pat. Nos. 4,432,134 issued Feb. 21, 1984, to Jones et al.; 4,242,419 issued Dec. 30, 1980, to Dayem et al.; 4,202,959 issued Sept. 2, 1980, to Kroger; and, 3,816,845 issued June 11, 1974, to Cuomo et al., give examples of superconducting Josephson junction configurations and processes for making them. Circuitry using Josephson junctions for analog-to-digital conversion is shown in U.S. Pat. No. 4,646,060 issued 2/24/87 to Phillips et al, U.S. Pat. No. 4,315,255 issued 2/9/82 to Harris and Hamilton, and U.S. Pat. No. 4,672,359 issued 6/9/87 to Silver. The operating parameters of DC SQUID's and a SQUID amplifier are described in U.S. Pat. No. 4,496,854 issued to Chi et al on 1/29/85. A paper entitled "100 GHz Binary Counter Based on DC SQUID", by Hamilton and Lloyd, IEEE Electron Device Letters, Vol. EDL-3, No. 11, pp 335-38, November 1982, describes the Josephson junction integrating counter circuit. The Hamilton et al circuit is the preferred counter for use with the instant invention.
The recent discovery by Muller and Bednorz of ceramic oxide superconductors which are superconductive at relatively high temperatures (e.g. now 90.degree. K. or above) has dramatically increased the interest in superconductivity and resulted in a large number of publications. The ceramic superconductors have generally been oxides of at least one rare earth (hereafter the term "rare earth" will be understood to include yttrium as well as the lanthanide elements, unless otherwise stated), at least one alkaline earth metal, and copper, although recently barium (or thallium), calcium, strontium, copper, oxide superconductors have been developed. For example, Willis et al. in a letter to the editor entitled "Superconductivity Above 90.degree. K. in Magnetic Rare Earth-Barium-Copper Oxides" (Journal of Magnetism and Magnetic Materials 67, 1987, North Holland, Amsterdam) report measurements of superconducting and magnetic behavior on samples which were prepared by sintering the rare earth oxide, copper oxide, and barium carbonate. Ceramic superconductors are very sensitive to oxygen content and the oxygen content is generally adjusted by the high temperature annealing. U.S. Pat. No. 4,804,649 issued to Sherif on 2/14/89 describes an oxalate precipitation process for forming metal oxide ceramic superconductors. British patent 2,202,528 A, published 9/28/88, describes superconducting oxide-metal composites (which also contain a noble metal) in a number of forms, including as a thin film. Infrared sensors using high temperature superconducting oxide ceramics is discussed in an article by Leung et al entitled "Optical detection in thin granular film of Y-Ba-Cu-O at temperatures between 4.2.degree. and 100.degree. K.", pages 2046-47, Applied Physics Letters, Vol. 50 (1987).